Synthesis of elastomeric poly(carborane-siloxane-acetelyene)s

ABSTRACT

Abstract of the Disclosure 
     A linear polymer comprising carborane, siloxane, and acetylene units, which may be cross-linked to a cured polymer and/or pyrolyzed to a ceramic.

Detailed Description of the Invention CROSS REFERENCE TO RELATEDAPPLICATIONS

This application is a divisional application of US Patent No. 6,967,233,which claims priority to U.S. Provisional Patent Application No.60/450,325 filed on 02/28/2003, both incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates generally to cross-linkable linear polymerscontaining carborane, siloxane, and acetylene groups, precursorsthereof, and elastomers, plastics, and ceramics made therefrom.

DESCRIPTION OF RELATED ART

The quest for high-temperature elastomers has been an evolving endeavor.An ever-increasing demand for such materials, especially in theaerospace industry, has served as a catalyst for continuing researchefforts. The desired properties of such elastomers include long-termthermal, thermo-oxidative, and hydrolytic stabilities to temperaturesapproaching 400°C, and flexibility to temperatures as low as -50°C.Poly(siloxane)s are known to exhibit good high temperature resistanceand excellent elasticity at low temperatures. Their elasticity isattributed to the pronounced conformational flexibility of their-Si-O-Si- backbone chain and to the ease of rotation around their Si-Obonds.

The thermal and oxidative properties of poly(siloxane) systems have beenfurther improved by the incorporation of carboranes in such systems. Thehigh chemical, thermal, and oxidative stabilities of carboranes can makethe resultant poly(carborane-siloxane) systems even more resilient athigh temperatures. The carboranes impart good protection againstoxidative degradation. Furthermore, it has been seen that theincorporation of acetylenes into the backbones ofpoly(carborane-siloxane) systems improves the ability of these systemsto retain their mass at very high temperatures. This is due to theacetylene-imparted ability to generate cross-linked centers, therebyreducing the preferences for skeletal cleavage of the backbone.

Polymers, ceramics, and precursors containing carborane, siloxane, andacetylene groups are disclosed in U.S. Patent Nos. 5,272,237; 5,292,779;5,348,927; 5,483,017; 5,756,629; 5,780,569; 5,932,335; 5,969,072;5,981,678; 6,187,703; 6,225,247; and 6,265,336, all incorporated hereinby reference.

U.S. Patent No. 5,348,917 to Keller et al. discloses acarborane-siloxane-acetylene polymer having the formula:

This polymer is made by reacting 1,4-dilithio-1,3-butadiyne with abis(chlorosiloxy)carborane. The polymer can be cross-linked betweenacetylene groups to a thermoset and pyrolyzed to a ceramic.

U.S. Patent No. 5,780,569 to Keller et al. discloses a copolymercontaining the above repeating unit and repeating units containingsiloxyl and acetylene groups, as in the formula:

This polymer is made by reacting 1,4-dilithio-1,3-butadiyne with abis(chlorosiloxy)carborane and a dichlorosiloxane. U.S. Patent No.5,483,017 to Keller et al. discloses that the polymer can becross-linked between acetylene groups to a thermoset and pyrolyzed to aceramic.

These polymers can have favorable thermal and oxidative properties. Theacetylene groups aid in maintaining the polymer's shape and mass at veryhigh temperatures. However, these polymers have a relatively high numberof acetylene groups versus siloxane and carborane groups. This resultsin a high degree of cross-linking that inhibits the natural flexibilityof the Si-O bonds. These cross-linked polymers are generally thermosets.

There is need for an elastomer having favorable thermal and oxidativeproperties. Such an elastomer may be useful in a variety of hightemperature applications as insulation for electrical wire and as enginecomponents. Polyimides are currently used as high temperatureinsulation; however, they readily decompose at 400°C in air.

BRIEF SUMMARY OF THE INVENTION

The invention comprises a linear polymer comprising the formula:

⁽¹⁾

wherein m, n, w, and z are independently selected integers greater thanor equal to 1; x and y are independently selected integers greater thanor equal to 0; q is an integer from 3 to 16; q' is an integer from 0 to16; each R and R' group is an independently selected organic group;(C≡C)_(m) represents an alkynylene group when m is 1 or conjugatedalkynylene groups when m is greater than 1; and CB_(q)H_(q')C is acarborane group.

The invention further comprises an cured polymer comprising the formula:

⁽²⁾

wherein m, n, w, x, y, z, q, q', R, R', and CB_(q)H_(q')C are as definedabove; and

represents a group made from an alkynylene group when m is 1 orconjugated alkynylene groups when m is greater than 1, crosslinked toanother such group.

The invention further comprises a siloxane-acetylene precursorcomprising the formula:

⁽³⁾

wherein m, w, x, R, and (C≡C)_(m) are as defined above; and X is ahalogen.

The invention further comprises a carborane-siloxane precursorcomprising the formula:

⁽⁴⁾

wherein y, z, q, q', R', and CB_(q)H_(q')C are as defined above, andwherein M is selected from the group consisting of Li, Na, K, and MgX',wherein X' is a halogen.

The invention further comprises a synthesis process comprising the stepsof: providing a siloxane-acetylene precursor as defined above and acarborane-siloxane precursor as defined above; and reacting thesiloxane-acetylene precursor with the carborane-siloxane precursor toform a linear polymer.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows DSC thermograms of disiloxane-containing linear polymers(2:3:1), (4:5:1), and (9:10:1) and a prior art polymer (1:2:1);

Fig. 2 shows TGA thermograms of disiloxane-containing linear polymers(2:3:1), (4:5:1), and (9:10:1) in a flow of nitrogen;

Fig. 3 shows DSC thermograms of showing the glass transitiontemperatures of disiloxane-containing cured polymers (2:3:1), (4:5:1),and (9:10:1); and

Fig. 4 shows DSC thermograms showing the glass transition temperaturesof trisiloxane-containing cured polymers (2:3:1), (4:5:1), and (9:10:1).

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

At a minimum the process comprises the steps of providing asiloxane-acetylene precursor and a siloxane-carborane precursor, andreacting them to form a linear polymer. The siloxane-acetylene precursorcontains halogens, and the siloxane-carborane precursor contains Li, Na,K, or MgX', wherein X' is a halogen.

Siloxane-Acetylene Precursor

The siloxane-acetylene precursor can have the structure shown above informula (3). Each R group is an independently selected organic groupincluding, but not limited to, saturated aliphatic, unsaturatedaliphatic, aromatic, and fluorocarbon groups. Using larger alkyl groupsfor the R groups may increase the solubility of the precursors inorganic solvents and increase the hydrophobicity and decrease thethermo-oxidative stability of linear polymers and cured polymers madeusing the precursor. Using aryl groups for the R groups may increase thestiffness and slightly increase the thermo-oxidative stability of linearpolymers made using the compound. The R groups can all be methyl groups.The X groups are not required to be the same halogen. Both X's can bechlorine. A suitable value for m is 2. A suitable average value for w is1.

Siloxane-acetylene precursors can be synthesized in a two-stepsynthesis. This synthesis is an example of providing asiloxane-acetylene precursor. The claimed process is not limited by thefollowing synthesis of a siloxane-acetylene precursor. The claimedcompounds are not limited to siloxane-acetylene precursors or productsthereof that are made by or may be made by this synthesis.

An acetylenic compound comprising the formula M-(C≡C)_(m)-M is obtained.M is selected from the group consisting of Li, Na, K, and MgX', whereinX' is a halogen. An example synthesis is to react four moles of n-butyllithium with hexachloro-1,3-butadiene to form 1,4-dilithio-1,3-butadiyneas in formula (1).

⁽⁵⁾

Similar reactions also produce acetylenic compounds with one or threeethynyl groups. Dilithioacetylene can be made by substitutingtrichloroethylene for hexachloro-1,3-butadiene in Formula (5). Disodiumsalt of 1,3,5-hexatriyne may be made according to the proceduredisclosed in Bock et al., "d-Orbital Effects in Silicon Substitutedπ-Electron Systems. Part XII. Some Spectroscopic Properties of Alkyl andSilyl Acetylenes and Polyacetylenes," J. Chem. Soc. (B), 1968, 10, 1158,incorporated herein by reference. Although there is no upper limit tothe value of m, suitable ranges include, but are not limited to, 1 to12, 1 to 10, 1 to 8, 1 to 6, 1 to 3, and 1 to 2.

Acetylenic derivatives having the general formula H-(C≡C)_(m)-H can beformed by the procedure disclosed in Eastmond et al., "Silylation as aProtective Method for Terminal Alkynes in Oxidative Couplings - AGeneral Synthesis of the Parent Polyynes," Tetrahedron, 1972, 28, 4601,incorporated herein by reference, and can be converted into dilithiosalts by reacting with n-butyllithium. Synthesis of the lower polyyneseries H-(C≡C)_(m)-H (n=2,3,4 and 5) is known to be based upon lowtemperature sodamide dehydrohalogenation ofα,ω-bis(chloromethyl)alkynes, ClCH₂-(C≡C)_(m-1)-CH₂Cl in liquid ammonia,a technique which provided a convenient route to diacetylene but whichproved increasingly troublesome for tri- and tetraacetylene.Pentaacetylene, the highest member of the series was obtained in ca. 1%yield from the precursor, ClCH₂-(C≡C)₄-CH₂Cl. Polyynes in the seriesH-(C≡C)_(m)-H (n=4,5,6,7,8,9,10 and 12) are known to have been preparedin solution by sequences involving Cu-catalyses oxidative couplings (Haytechnique) of silyl-protected terminal alkynes, partial cleavage(desilylation) of the products by alkali, recoupling and completedesilylation. Thus using conditions established in a model couplingEt₃Si-C≡C-H (I) → Et₃Si-(C≡C)₂-SiEt₃ (II), coupling of the silyldiyneEt₃Si-(C≡C)₂-H (III) gives Et₃S-(C≡C)₄-SiEt₃ (IV) which upon controlledcleavage yields a chromatographically separable mixture ofEt₃S-(C≡C)₄-SiEt₃ (IV), Et₃Si-(C≡C)₄-H (V) and H-(C≡C)₄-H (VI). Couplingof Et₃Si-(C≡C)₄-H (V) in turn gives Et₃Si-(C≡C)₈-SiEt₃ (VII) which uponcleavage yields Et₃Si-(C≡C)₈-H (VIII) and H-(C≡C)₈-H (IX) and couplingof Et₃Si-(C≡C)₈-H (VIII) gives the bissilylhexadecaacetyleneEt₃Si-(C≡C)₁₆-SiEt₃ (X).

Hexa-acetylene may be synthesized analogously:

Et₃Si-(C≡C)₃-SiEt₃ (XII) → Et₃Si-(C≡C)₃-H (XI)

Et₃Si-(C≡C)₃-H (XI) → Et₃Si-(C≡C)₆-SiEt₃ (XIII)

Et₃Si-(C≡C)₆-SiEt₃ (XIII) → Et₃Si-(C≡C)₆-H (XIV)

Et₃Si-(C≡C)₆-H (XIV) → H-(C≡C)₆-H (XV)

Dodeca-acetylene may be synthesized analogously:

Et₃Si-(C≡C)₆-H (XIV) → Et₃Si-(C≡C)₁₂-SiEt₃ (XVI)

Et₃Si-(C≡C)₁₂-SiEt₃ (XVI) → H-(C≡C)₁₂-H (XVII)

Other exemplary members of the series are prepared via mixed couplings:

(I)+(V) → Et₃Si-(C≡C)₅-SiEt₃ (XVI) → H-(C≡C)₅-H (XIX)

(I)+(XIV) → Et₃Si-(C≡C)₇-SiEt₃ (XX) → H-(C≡C)₇-H (XXI)

(I)+(VIII) → Et₃Si-(C≡C)₉-SiEt₃ (XXII) → H-(C≡C)₉-H (XXIII)

(III)+(VIII) → Et₃Si-(C≡C)₁₀-SiEt₃ (XXIV) → H-(C≡C)₁₀-H (XXV).

A dihalopolysiloxane may be made by reacting a dihalosilane with itselfin the presence of water and diethylether to make a dihalodisiloxylcontaining compound as shown in formula (2). Repeated reaction with thedihalosilane will add additional siloxyl groups and increase the valueof x. Some dihalopolysiloxanes are also commercially available. Althoughthere is no upper limit to the value of x or y, suitable ranges include,but are not limited to, at least 1, 1 to 1000, 1 to 500, 1 to 250, 1 to10, 1 to 5, and 1 to 2.

⁽⁶⁾

The butadiyne or other acetylenic compound may then be reacted with thedihalopolysiloxane (or dihalosilane when x is 0) to form thesiloxane-acetylene precursor as shown in formula (3). The reaction mayoccur spontaneously at room temperature or below room temperature. WhenM is MgX', such as MgBr, the reaction is a Grignard reaction. An excessof the siloxyl compound is used so that the precursor is capped by thesiloxyl moiety on both ends. The average value of w is determined by theratio of dihalopolysiloxane to acetylenic compound. The closer the ratiois to 1, the larger the value of w. A 2:1 ratio or higher results in anaverage value of w of about 1. It is also possible to use combinationsof different acetylenic compounds and polysiloxanes, such that in somemolecules there are multiple values for m and x.

⁽⁷⁾

An example of this reaction is shown in formula (4), where m is 2, w is1, x is 1, the halogen is chlorine, and all R groups are methyl groups.All compounds used are commercially available products. Other values andsubstituents are also possible. Compounds used in other embodiments mayalso be commercially available or may be synthesized according to knowntechniques.

⁽⁸⁾

If only one dihalopolysiloxane compound is used, this process of makingthe siloxane-acetylene precursor produces a compound with at most 2(x+1)different R groups. Each polysiloxane unit in the precursor will havethe same set of R groups in the same arrangement. However, if thepolysiloxane unit is asymmetrical, it may be added in either of twomirror image orientations. This is exemplified in formula (5), where xis 1, and w is 2. When mixtures of different dihalopolysiloxanes areused, the result may be a mixture of siloxane-acetylene precursors, someof which may have all different R groups. This is shown in formula (6).

⁽⁹⁾

⁽¹⁰⁾

Siloxane-Carborane Precursor

The siloxane-carborane precursor, as shown in formula (4), can be madeby reacting an excess amount of dilithiocarborane with adihalopolysiloxane (or dihalosilane when y is 2). The claimed process isnot limited by the following synthesis of a siloxane-carboraneprecursor. The claimed compounds are not limited to siloxane-carboraneprecursors or products thereof that are made by or may be made by thissynthesis.

A dilithiocarborane may be made as shown in formula (7). Othercarboranes may also be used in this reaction. The carborane may havesubstituents other then lithium. The general formula isM-CB_(q)H_(q')C-M, where M is selected from the group consisting of Li,Na, K, and MgX', wherein X' is a halogen. The reaction to make thesiloxane-carborane precursor is shown in formula (8). The siloxanecompound may be made as described above, and suitable values for y arethe same as for x. The reaction may occur spontaneously at roomtemperature or below room temperature. When M is MgX', such as MgBr, thereaction is a Grignard reaction. An excess of dilithiocarborane is used.It is also possible to use combinations of different carboranes andpolysiloxanes, such that in some molecules there are multiple values forq, q', and y.

⁽¹¹⁾

⁽¹²⁾

Each R' group is an independently selected organic group including, butnot limited to, saturated aliphatic, unsaturated aliphatic, aromatic,and fluorocarbon groups. All R' groups can be methyl groups. The Xgroups are not required to be the same halogen. Both X's can bechlorine. It is to be understood that the formula CB_(q)H_(q')C includescarboranes in which one or more or all of the hydrogen atoms arereplaced with other functional groups including, but not limited to,alkyl and halogen groups. An alternative structure encompassed byCB_(q)H_(q')C is CB_(q)H_(q')X_(q'')R_((q-q'-q''))C. Suitable carboranegroups include, but are not limited to, 1,7-dodecacarboranyl(1,7-C₂B₁₀H₁₀, m-carborane); 1,10-octacarboranyl (1,10-C₂B₈H₈);1,6-octacarboranyl (1,6-C₂B₈H₈); 2,4-pentacarboranyl (2,4-C₂B₅H₅);1,6-tetracarboranyl (1,6-C₂B₄H₄); 9-alkyl-1,7-dodecacarboranyl(9-alkyl-1,7-C₂B₁₀H₉); 9,10-dialkyl-1,7-dodecacarboranyl(9,10-dialkyl-1,7-C₂B₁₀H₈); 2-alkyl-1,10-octacarboranyl(2-alkyl-1,10-C₂B₈H₇); 8-alkyl-1,6-octacarboranyl (8-alkyl-1,6-C₂B₈H₇);decachloro-1,7-dodecacarboranyl (1,7-C₂B₁₀Cl₁₀);octachloro-1,10-octacarboranyl (1,10-C₂B₈Cl₈);decafluoro-1,7-dodecacarboranyl (1,7-C₂B₁₀F₁₀);octafluoro-1,10-octacarboranyl (1,10-C₂B₈F₈);closo-dodeca-orthocarboranyl; closo-dodeca-metacarboranyl; andcloso-dodeca-paracarboranyl. The examples use 1,7-dodecacarboranyl(m-carborane), so that q and q' are both 10. m-Carborane and p-carboranemay react faster than o-carborane.

The value of z depends on the stoichiometric ratio of dilithiocarboraneto dihalopolysiloxane. A ratio of 2:1 will result in an average value ofz of about 1, as in formula (9). A ratio of 3:2 will result in anaverage value of z of about 2 as in formula (10). All compounds used arecommercially available products. Reactants used in other embodiments mayalso be commercially available or may be synthesized according to knowntechniques. Other values and substituents are also possible.

(13)

⁽¹⁴⁾

The smaller the ratio, the larger the value of z. This results in alinear polymer having more carborane units and more total siloxane unitsrelative to the acetylene groups. If only one dihalopolysiloxanecompound is used, this process of making the siloxane-acetyleneprecursor produces a compound with at most 2(y+1) different R' groups.Each polysiloxane unit in the precursor will have the same set of R'groups in the same arrangement. However, if the polysiloxane unit isasymmetrical, it may be added in either of two mirror imageorientations, as described above for the siloxane-acetylene precursor.When mixtures of different dihalopolysiloxanes are used, the result maybe a mixture of siloxane-carborane precursors, some of which may haveall different R' groups.

Linear Polymer

The siloxane-acetylene precursor is reacted with the carborane-siloxaneprecursor to form a linear polymer as shown in formula (11). Thereaction may occur spontaneously at room temperature or below roomtemperature. When M is MgX', such as MgBr, the reaction is a Grignardreaction. The claimed compounds are not limited to linear polymers thatare made by or may be made by this process. A high molecular weightlinear polymer may be formed by using a 1:1 or near 1:1 stoichiometricratio of the two precursors. Formula (12) shows the general formula forthe linear polymer when the initial reactants are m-carborane,1,4-dilithio-1,3-butadiyne, and polysiloxanes fully substituted withmethyl groups, and where w is 1.

⁽¹⁵⁾

⁽¹⁶⁾

A given linear polymer may be partially described by the molar ratios ofthe three types of functional groups in the repeat unit. A (2:3:1)linear polymer has a repeat unit having 2 carborane units, 3polysiloxane units, and 1 acetylenic unit. This corresponds to z=1. Thisnomenclature does not describe the values of m, x, y, q, q', or the Rand R' groups. When z is 3, the ratio is (4:5:1), and when z is 8, theratio is (9:10:1). As z increases, the fraction of acetylenic groupsdecreases. There is no upper limit on the value of z. However, asuitable range includes, but is not limited to, 1 to 10. There is noupper limit on the value of n. However, a suitable range of molecularweight includes, but is not limited to, about 10,000 to about 50,000.

Cured Polymer

The linear polymer may have only one acetylenic group, having one ormore acetylenes, in the repeat unit. This can allow for the formation ofan elastomer upon cross-linking, although some embodiments form athermoset or plastic. Elastomers, plastics, and thermosets can alsoresult from linear polymers having more than one acetylenic group. Asused herein, the term "cured polymer" includes all such elastomers,plastics, and thermosets. The formula for the cured polymer is as shownabove in formula (2).

The conversion of the linear polymer to the cured polymer can beaccomplished by exposing the linear polymer to heat or light. Thermalconversion of the carbon-to-carbon triple bonds in the linear polymer toform the cured polymer is dependent on both the curing temperature andthe curing time. The heating of the linear polymer can be carried outover a curing temperature range and time sufficient for thecross-linking of the carbon-to-carbon triple bonds of the individuallinear polymers, resulting in the formation of a single mass of curedpolymer. In general, the curing time may be inversely related to thecuring temperature. Suitable temperature ranges include, but are notlimited to, 150-450°C, 200-400°C, 225-375°C, and 250-350°C. Heating totemperatures of 600-700°C may convert m-carborane groups in the curedpolymer to p-carborane groups, as well as convert the material to aceramic mass. Suitable curing time ranges include, but are not limitedto, 1-48 hours, 2-24 hours, 8-12 hours, and 1-8 hours.

The photocross-linking process, of converting the carbon-to-carbontriple bonds of the linear polymer into unsaturated cross-linkedmoieties necessary for forming the cured polymer, is dependent on boththe exposure time and the intensity of the light used during thephotocross-linking process. Ultraviolet (UV) light is a suitable type oflight to use during the photocross-linking process. The exposure time ofthe linear polymer to the UV light may be inversely related to theintensity of the UV light used. The exposure time, intensity, andwavelength of the UV or other light used is that sufficient for thecarbon-to-carbon triple bonds of the linear polymer to be cross linkedto form the cured polymer. Suitable exposure times include, but are notlimited to, 1-100 hours, 24-36 hours, 12-24 hours, and 4-8 hours.

The linear polymers can exhibit sufficiently low viscosities either atroom temperature or at higher temperatures below the polymerizationtemperature to readily fill complex dies or shapes for forming partstherefrom. The resulting cured polymers can retain the shape of the dieor mold.

Formula (13) shows a portion of an example cured polymer. It is notrequired that every acetylenic carbon be cross-linked as shown. Thestructure shown is not intended to be representative of all possiblecross-links. The cross-linked acetylenic moiety may include severaldifferent cross-linking structures such as those shown in formula (14).

⁽¹⁷⁾

⁽¹⁸⁾

The acetylenic functionality may provide advantages relative to othercross-linking centers. An acetylenic moiety remains inactive duringprocessing at lower temperatures and reacts thermally to form conjugatedpolymeric cross-links without the evolution of volatiles.

The properties of the cured polymers will depend on the distanceseparating the cross-linking centers. The concentration of theacetylenic units may dictate the extent of cross-linking and hence, theresultant freedom for the -Si-O-Si- backbone flexibility. In addition,an increase in the density of Si-O units and a reduction in theacetylenic units may also improve the elasticity of such systems. Inpoly(siloxane)s, a linear relationship can exist between the densitiesof Si-O units and the glass transition temperatures. The cured polymermay also be useful as a protective coating on fibers.

Disiloxane polymers may have greater thermal stability in comparison tothe trisiloxane polymers, as such has been well established forcorresponding poly(carborane-siloxane) systems (Peters,"Poly(dodecacarborane-siloxanes)," J. Macromol. Sci.-Rev. Macromol.Chem. and Phys., 1979, C17(2), 173, incorporated herein by reference).This is demonstrated in the examples. Additionally, the thermalstability of the disiloxane polymers, relative to the trisiloxanesystems, may be enhanced due to the slightly shorter distance betweenthe cross-linking centers. This may be due to the greater concentrationof acetylenes in their backbones, whereas in the trisiloxane systems,the distance between successive acetylene units is slightly longer.

The greater density of the -Si-O- groups in the trisiloxane systems mayhave the beneficial effect of conferring improved elasticity whencompared to their disiloxane counterparts. In fact, this advantage ismanifested in the glass transition temperatures of these systems. Theglass transition temperatures of the disiloxane and the trisiloxanesystems are found to be in the range of 56°C to 35°C and -35°C to -47°C,respectively (Table 3). In both systems, the Tg values of the threeconstituent members of a series are found to decrease with a reductionin concentration of the acetylenic units. The (9:10:1) polymers in thetrisiloxane and disiloxane systems, with the lowest acetyleneconcentration, were observed to exhibit the lowest Tg values of -47°Cand 35°C, respectively. Similarly, for the (2:3:1) polymers, thetrisiloxane- and the disiloxane-cured cured polymers were found to showthe highest Tg's with values of -35°C and 56°C. Hence, at roomtemperature, the data indicates that the trisiloxane- and thedisiloxane-cured systems exhibit elastomeric and plasticcharacteristics, respectively.

Ceramic

A ceramic may be made by heating or pyrolyzing the linear polymer orcured polymer. This may be done in a single step of heating the linearpolymer, or the linear polymer may be converted to the cured polymer,followed by heating to form the ceramic. Suitable pyrolyzing conditionsinclude, but are not limited to, 450-2750°C in an inert atmosphere, suchas N₂, and 450-1650°C in an oxidizing atmosphere, such as air. Theheating may be done at 1 atm pressure; however, the heating temperaturesmay be varied with the pressure. Thus, when the pressure is less than 1atm, for example, under a vacuum, the heating range can be reducedsufficiently to drive off volatiles and to convert to the ceramic.

The linear polymer may be poured into a mold and heated between150-450°C to form the cured polymer either in conjunction with anotherfiller material or reinforcing fibrous material, to add structuralstrength, or without such additive materials to form a solid orcomposite product. Upon pyrolyzing, the material can maintain the shapeof the original mold. One advantage of making the ceramic is that it canbe readily formed into various shapes due to the liquid state of thelinear polymer at room temperature or at the melting point, and the easeof converting the linear polymer into the cured polymer by heating, andthen into the ceramic by continued heating.

In an inert atmosphere, suitable pyrolyzing temperature ranges include,but are not limited to, 450-2750°C, 450-2000°C, 450-1500°C, and450-1300°C. In an oxidizing atmosphere, suitable pyrolyzing temperatureranges include, but are not limited to, 450-1650°C, 450-1500°C,450-1350°C, and 450-1100°C. Generally, the heating rate is that heatingrate which is sufficient to drive off any volatile compounds and to formthe desired ceramic. The heating rate is not a limiting factor of thepresent invention. However, suitable heating rate ranges include, butare not limited to, 0.01-200°C/min, 0.01-100°C/min, 0.01-50°C/min, and0.01-25°C/min. Similarly, the cooling rate may be sufficient to cool theformed ceramic without causing significant thermal stresses orsignificant reduction in structural integrity of the formed ceramic. Thecooling rate of the formed ceramic is not a limiting factor of thepresent invention. However, suitable cooling rate ranges include, butare not limited to, 0.01-200°C/min, 0.01-100°C/min, 0.01-50°C/min, and0.01-25°C/min.

Having described the invention, the following examples are given toillustrate specific applications of the invention. These specificexamples are not intended to limit the scope of the invention.

General conditions -Unless otherwise noted, all syntheses were performedunder an atmosphere of dry argon utilizing standard Schlenk techniques.m-Carborane (m-CB; Olin) was sublimed prior to use. n-Butyl lithium(n-BuLi; Aldrich) was titrated before use. Lithium diisopropylamide(LDA; Aldrich) was used as received. Hexachlorobutadiene (C₄Cl₆),dichlorotetramethyldisiloxane (DCTMDS), anddichlorohexamethyltrisiloxane (DCHMTS) (all from Aldrich) were distilledbefore use. Anhydrous THF (99.9%; Aldrich) and diethyl ether (Et₂O;Aldrich) were used as received. The preparation of1,4-dilithio-1,3-butadiyne was an adaptation from Ijadi-Magsooke et al.,"Synthesis and study of silylene-diacetylene polymers," Macromolecules1990, 23, 4485, incorporated herein by reference. Thermogravimetricanalyses (TGA) were performed on a SDT 2960 Simultaneous DTA-TGAanalyzer. The DSC studies were performed on a DSC 2920 Modulated DSCinstrument. Unless otherwise mentioned, all thermal experiments werecarried out with heating rates of 10°C/min (both TGA and DSC) andnitrogen flow rates of 100 cc/min. Infrared spectra were obtained on aNicolet Magna 750 Fourier Transform infrared (FTIR) spectrophotometer.¹H and ¹³C NMR spectra were acquired on a Bruker AC-300 spectrometer andreferenced to the internal solvent peak.

Example 1

Synthesis of chlorodisiloxane-capped acetylene - A flame-dried 250 mLSchlenk flask, under argon, was charged with 10 mL of THF and was cooledto -78°C by isopropanol/dry ice. n-BuLi (2.77 mL of 2.5 M solution inhexanes, 6.92 mmol, 4 eq.) was added slowly to the THF. After 10 min,C₄Cl₆ (0.27 mL, 1.73 mmol) was added drop wise over 10 min. Theresultant gray-brown slurry was warmed to room temperature and stirredfor 3 hours. After this period, the mixture was cooled again to -78°Cand DCTMDS (0.68 mL, 3.46 mmol) was added drop wise via a gas-tightsyringe. The mixture was then warmed to room temperature and stirred for2 hours, resulting in the formation of a large amount of whiteprecipitate (LiCl).

Example 2

Synthesis of lithiated m-carborane-capped disiloxane - In a 250 mLflame-dried flask, under argon, m-CB (0.5g, 3.47 mmol) was dissolved in1 mL of THF and cooled to -78°C. LDA (3.5 mL, 7.01 mmol) was addeddropwise to the solution resulting in the formation of a reddish orangesolid. On warming the mixture to room temperature, the solidre-dissolved in THF. At this point, the volatiles were removed undervacuum. The residue was re-dissolved in 2 mL of THF and the mixture wascooled to 0°C. To this solution, DCTMDS (0.34 mL, 1.73 mmol) was addeddropwise via a gas-tight syringe. The mixture was stirred for 3 hours.

Example 3

Synthesis of (2:3:1) poly(carborane-disiloxane-acetylene) linearpolymer - The solution resulting from Example 1 was cannulated into theflask containing the result of Example 2. The mixture was stirredfurther for 2 hours. At this time, a few drops of DCTMDS were added tothe mixture and the stirring was continued for an additional hour. Oncethe stirring was completed, the mixture was poured into 50 mL of coldsaturated NH₄Cl and was extracted three times with 75 mL each of Et₂O.The Et₂O extracts were combined, washed with 100 mL brine, and driedover anhydrous Na₂SO₄. The dried extracts were filtered through aone-inch pad of Celite and the solvents were removed under vacuum. Adark brown viscous oil was obtained.

Example 4

Synthesis of other poly(carborane-disiloxane-acetylene) linear polymers-Other linear polymers were synthesized using similar procedures. Table1 shows the amounts in mmol of the reagents used. Ratios of (2:3:1),(4:5:1), and (9:10:1) were made using both a disiloxane and atrisiloxane. All of the syntheses of Examples 3 and 4 proceeded to highyields (85-95%) of the linear polymers, which were viscous brown oils.The disiloxane products appeared more viscous than the trisiloxanesystems, presumably because of the lesser flexibility of the -Si-O-Si-backbone relative to the -Si-O-Si-O-Si- backbone.

TABLE 1 siloxane-acetylene precursor siloxane-carborane precursor DCTMDSor DCTMDS or C_(4Cl) ₆ n-BuLi DCHMTS m-CB LDA DCHMTS (2:3:1) 1.73 6.923.46 3.47 7.01 1.74 (4:5:1) 0.86 3.44 1.73 4.36 8.81 3.47 (9:10:1) 0.381.52 0.76 4.82 9.74 4.50

The progress of the reactions with DCTMDS was monitored by FTIR and NMRcharacterization studies. The appearance and growth of the diacetylenemoiety at 2075 cm⁻¹ and the complete disappearance of the butadiene bandin the FTIR spectrum indicated that the reaction had proceeded tocompletion. Other prominent absorptions exhibited by the productsinclude the peaks at 2963 (C-H), 2600 (B-H), 1081 (strong Si-O-Sistretching), and at 1260, 840, and 810 (strong Si-C deformation) cm⁻¹.The intensity of the diacetylenic stretch at 2070 cm⁻¹ decreased as zbecame larger. The diacetylenic and siloxyl methyl carbons were alsoidentified by the resonances at 88-85 and 2-0 ppm, respectively, in the¹³C NMR spectra. The ¹H NMR spectra for the linear polymers showedsiloxyl methyl and B-H resonances between 0.4-0.0 and 3.5-1.0 ppm,respectively. Table 2 exhibits the FTIR and NMR (¹H and ¹³C) absorptionsof the three polymers.

TABLE 2 Polymer IR (cm⁻¹⁾ ^(a) ^(1H NMR) ^(b) ^(13C NMR) ^(c) (2:3:1)2072(s) 0.27(s), 021(s), 0.18(s), 0.12(s), 1.79, 1.00, 0.52, 0.26disiloxane (C≡C–C≡C) 0.08(s), (0.05)(s) (Si–(CH₃₎ ₂₎ (Si–(CH₃₎ ₂₎2972(s) (C–H) 3.25-0.72(br) (CB_(10H) _(10C)) 65.92 (CB_(10H) _(10C))2606(vs, br) 86.8, 84.2 (C≡C–C≡C) (B–H) 1074(vs, br) (Si–O–Si) 1267(vs),841(s), 804(vs, br) (Si–C) (4:5:1) 2073(s) 0.28(s), 022(s), 0.17(s),0.12(s), 1.80, 1.02, 0.53, 0.29 disiloxane (C≡C–C≡C) 0.09(s), (0.05)(s)(Si–(CH₃₎ ₂₎ (Si–(CH₃₎ ₂₎ 2969(s) (C–H) 3.25-0.72(br) (CB_(10H) _(10C))65.90 (CB_(10H) _(10C)) 2602(vs, br) 87.0, 84.6 (C≡C–C≡C) (B–H) 1071(vs,br) (Si–O–Si) 1268(vs), 842(s), 805(vs, br) (Si–C) (9:10:1) 2075(s)0.26(s), 021(s), 0.16(s), 0.11(s), 1.80, 1.00, 0.47, 0.29 disiloxane(C≡C–C≡C) 0.07(s), (0.04)(s) (Si–(CH₃₎ ₂₎ (Si–(CH₃₎ ₂₎ 2969(s) (C–H)3.25-0.72(br) (CB_(10H) _(10C)) 65.86 (CB_(10H) _(10C)) 2602(vs, br)87.4, 84.8 (C≡C–C≡C) (B–H) 1070(vs, br) (Si–O–Si) 1264(vs), 839(s),801(vs, br) (Si–C)^(aRelative intensities: vs-very strong, s-strong, m-medium, w-weak, br-broad.)^(bIn parts per million relative to SDCl)_(3 peak. Multiplicities: s-singlet, br-broad.)^(cIn parts per million relative to central CDCl) _(3 peak.)

Example 5

Formation and thermal properties of cured polymers - DSC runs of bothsets of polymers (disiloxyls and trisiloxyls) indicated that thecross-linking of the acetylenes to form network systems occurred between275-350°C. Based on this data, all the samples were cured at 250°C for30 min and further at 350°C for 60 min under N₂ to facilitate theircomplete conversion into cross-linked network systems. The cured sampleswere then heated under N₂ to 1000°C to test their thermal stabilities(Fig. 2). Between the sets, the disiloxane oligomers were found to bemore stable than the trisiloxane oligomers on heating to 1000°C (SeeTable 3). Additionally, in a set, the linear polymer that had thegreatest concentration of acetylenic groups exhibited the greatestretention of weight. Similarly, the thermal stabilities of the other twocured systems, within a set, decreased proportionally with the degree ofacetylene concentration.

TABLE 3 disiloxyl trisiloxy char yield/Tg char yield/Tg (2:3:1) 75%/56°C. 68%/−35° C. (4:5:1) 72%/45° C. 63%/−43° C. (9:10:1) 52%/35° C.41%/−47° C.

Example 6

Thermal Properties - The thermal properties of the three polymers madefrom DCTMDS were studied by DSC analysis. The DSC thermograms indicatedthat the cross-linking of the diacetylene units to form a network systemoccurred between 275-380°C. The DSC plots for the polymers are shown inFig. 1 as well as (1:2:1) poly(m-carborane-disiloxane-diacetylene),shown in Formula (15), for comparison. The DSC exotherms for (2:3:1) and(4:5:1) peaked at 350°C and 359°C, respectively. The exotherm maximum of(9:10:1) was not as pronounced and did not show a clear maximum asobserved for (2:3:1) and (4:5:1), presumably due to the lowerconcentration of diacetylene units in this system. However, the onset ofcuring for (9:10:1) occurred at about the same temperature as in (2:3:1)and (4:5:1). These values were greater than the exotherm maximum valueof 341°C of (1:2:1). The lower concentration of diacetylene units in the(2:3:1), (4:5:1), and (9:10:1) systems may have required a higher curingtemperature than (1:2:1) to facilitate the 1,4-addition reaction of thediacetylenes. The propensity for the 1,4-addition reaction in thesediacetylene-diluted systems also may have suffered due to the greaterconcentration of carboranes when compared to (1:2:1). The carboraneunit, being electron withdrawing, makes the 1,4-addition reactionsthermodynamically less favorable. This trend was also borne out in themuch lower Tg value (289°C) for the acetylene-rich (1:2:1). The (1:2:1),with the highest concentration of diacetylene units, has the mostintense exotherm, and (9:10:1), with the lowest diacetyleneconcentration, has a greatly reduced exotherm.

⁽¹⁹⁾

Example 7

Thermal properties of chars - The thermo-oxidative stabilities of thecharred materials were also studied. Samples of the three cured polymersmade using DCTMDS that had been heated to 1000°C in N₂ were thermallytreated in air to 1000°C. After their oxidative exposure, the charsof(2:3:1), (4:5:1), and (9:10:1) gained 0.8%, 2.8% and 6.2% in weight,respectively. The major extent of weight increase occurred between 800°Cand 1000°C. Samples of the corresponding linear polymers were alsoheated directly in air. In the case of (9:10:1), there was a dramaticweight increase (about 5%) above 650°C, which was absent for (2:3:1) and(4:5:1). The enhanced oxidation for (9:10:1) may be due to a lowercross-linked density resulting in a larger amount of free volume, whichallowed oxygen to penetrate more easily into the char. Such a featurewould expose the borosilicates, formed during the heat treatment, tooxidation relative to the other two more densely cross-linked systems.This may also explain the greater gain (6.2%) of the char from (9:10:1)on exposure to oxygen as compared to (2:3:1) (0.8 %) and (4:5:1) (2.8%).

Example 8

Glass transition studies - DSC analysis was used to determine the Tg ofthe cured polymers made using DCTMDS. The linear polymerswere initiallyheated under N₂ at 250°C for 30 min and further at 400°C for two hours.The resulting cured polymers were then cooled to -70°C and heated at10°C/min to 150°C. The Tg values of the three systems were found todecrease proportionally with a reduction in concentration of thecrosslinked centers. Cured polymers (2:3:1), (4:5:1), and (9:10:1)exhibited Tg values (Fig. 3 and Table 3) of 56, 45, and 36°C,respectively. For comparison, the Tg values of linearpoly(disiloxane-carborane) and the cured poly(disiloxane-diacetylene)are 25 and 144°C, respectively. Hence, it appears that the incorporationof the diacetylene units into the poly(disiloxane-carborane)s came atthe expense of their elasticity. The observed Tg values indicate thatthe cured polymers have plastic characteristics at room temperature.

The Tg of the cured polymers made using DCHMTS was also determined.Poly(trisiloxane-carborane) and poly(disiloxane-carborane) have Tgvalues of -50°C and 25°C, respectively. Hence, a longer spacer resultingin an increase in the siloxyl concentration in thepoly(m-carborane-siloxane-diacetylene) systems could produce a similarreduction in the Tg values. The Tg results are shown in Fig. 4 and Table3. The trisiloxane cured polymers have lower Tg's and are cured polymersat room temperature.

Example 9

Coating of Zylon fiber with cured polymers to protect againstoxidation - A coating solution was prepared by dissolving 0.5 g oftrisiloxyl linear polymer (4:5:1) in 5 mL of CH₂Cl₂. A tow of Zylonfibers (an organic polymeric fiber) was cut into small pieces (~ 0.5inch, ~ 10 mg in weight) and initially dried at about 400°C for 4 hr inN₂ in a TGA apparatus to ensure the expulsion of moisture. The Zylontows were subsequently stored in a desiccator for later usage. Afterdrying and weighing, a tow was immersed in a vial containing a portionof the prepared solution for 5 minutes. At this time, the excesssolution was drained off and the vial with the coated tow was placedover a hot air blow dryer for 40 sec to drive away any residual CH₂Cl₂and was then weighed to obtain the weight of the coating. The coatedfiber was then cured at 250°C for 30 min and at 400°C for 2 hr in N₂. Itwas weighed again to see whether any weight was lost during the curingof the coated Zylon tow. The weight loss during curing was found to benegligible. This procedure was repeated three times, which was found toprotect the Zylon against oxidation upon subsequent heating to 1000°C inair. Using this concentration, three coatings and curing to 400°C werenecessary for complete protection. The number of coating layers fortotal protection would depend on the concentration of the coatingsolution.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is therefore to beunderstood that the claimed invention may be practiced otherwise than asspecifically described.

1. A cured polymer comprising the formula:

wherein m, n, w, and z are independently selected integers greater thanor equal to 1; wherein x and y are independently selected integersgreater than or equal to 0; wherein q is an integer from 3 to 16;wherein q' is an integer from 0 to 16; wherein each R group is anindependently selected organic group; wherein each R' group is anindependently selected organic group; wherein

represents a group made from an alkynylene group when m is 1 orconjugated alkynylene groups when m is greater than 1, crosslinked toanother such group; and wherein CB_(q)H_(q')C is a carborane group. 2.The cured polymer of claim 1, wherein every R group and every R' groupis methyl.
 3. The cured polymer of claim 1, wherein m is
 2. 4. The curedpolymer of claim 1, wherein x and y are independently selected integersgreater than or equal to
 1. 5. The cured polymer of claim 1, wherein xand y are independently selected from the group consisting of 1 and 2.6. The cured polymer of claim 1, wherein the average value of w isabout
 1. 7. The cured polymer of claim 1, wherein the average value of zis from 1 to
 10. 8. The cured polymer of claim 1, wherein q and q' are10.
 9. The cured polymer of claim 1, wherein CB_(q)H_(q')C ism-carborane.
 10. The cured polymer of claim 1, further comprising afiber, wherein the cured polymer forms a coating on the fiber.
 11. Aceramic made by heating the cured polymer of claim
 1. 12. Asiloxane-acetylene precursor comprising the formula:

wherein m and w are independently selected integers greater than orequal to 1; wherein x is an integer greater than or equal to 0; whereineach R group is an independently selected organic group; wherein X is ahalogen; and wherein (C≡C)_(m) represents an alkynylene group when m is1 or conjugated alkynylene groups when m is greater than
 1. 13. Thesiloxane-acetylene precursor of claim 12, wherein every R group ismethyl.
 14. The siloxane-acetylene precursor of claim 12, wherein X isCl.
 15. The siloxane-acetylene precursor of claim 12, wherein m is 2.16. The siloxane-acetylene precursor of claim 12, wherein x is aninteger greater than or equal to
 1. 17. The siloxane-acetylene precursorof claim 12, wherein x is selected from the group consisting of 1 and 2.18. The siloxane-acetylene precursor of claim 12, wherein the averagevalue of w is about
 1. 19. A carborane-siloxane precursor comprising theformula:

wherein z is an integer greater than or equal to 1; wherein y is aninteger greater than or equal to 0; wherein q is an integer from 3 to16; wherein q' is an integer from 0 to 16; wherein M is selected fromthe group consisting of Li, Na, K, and MgX', wherein X' is a halogen;wherein each R' group is an independently selected organic group; andwherein CB_(q)H_(q')C is a carborane group.
 20. The carborane-siloxaneprecursor of claim 19, wherein M is Li.
 21. The carborane-siloxaneprecursor of claim 19, wherein every R' group is methyl.
 22. Thecarborane-siloxane precursor of claim 19, wherein y is an integergreater than or equal to
 1. 23. The carborane-siloxane precursor ofclaim 19, wherein y is selected from the group consisting of 1 and 2.24. The carborane-siloxane precursor of claim 19, wherein the averagevalue of z is from 1 to 10
 25. The carborane-siloxane precursor of claim19, wherein q and q' are
 10. 26. The carborane-siloxane precursor ofclaim 19, wherein CB_(q)H_(q')C is m-carborane.